Potty Training

I need help. I can't believe that after potty training all 3 of my kids and 4 of my grandkids that I am stumped at what to do with my 3 year old grandson. He absolutely WILL NOT cooperate. He screams, clamps his legs together, stiffens up, bawls his head off, hits me, and just absolutely REFUSES to go to the toilet. Sawyer, who is not even 2 loves to sit on the potty and actually does his business! Jaxson, on the other hand, is beginning to look like he might be 30 years old before he is potty trained. I honestly don't know what to do with him. I know it's a battle of wills but he actually told me today that it's scary. He likes to flush after someone else uses the toilet. It doesn't bother him to get close to it or even sit on it if the lid is down. But, he won't stand next to it to go pee and he won't sit on the seat - with or without a child's potty ring.

Any suggestions?